CVE-2025-48812 is a medium-severity vulnerability classified as an out-of-bounds (OOB) read (CWE-125) affecting Microsoft Office Online Server, specifically version 1.0.0. The vulnerability arises from improper bounds checking in the processing of Microsoft Office Excel files within the Office Online Server environment. An unauthorized attacker can exploit this flaw to perform an out-of-bounds read, which allows them to disclose sensitive information from the server's memory. The vulnerability requires local access (AV:L) to the affected system, does not require privileges (PR:N), but does require user interaction (UI:R), such as opening a malicious Excel file via the Office Online Server interface. The impact is limited to confidentiality (C:H), with no impact on integrity or availability. The CVSS v3.1 base score is 5.5, reflecting a medium severity level. No known exploits are currently reported in the wild, and no patches have been published at the time of analysis. The vulnerability was reserved in May 2025 and published in July 2025. Given the nature of Office Online Server as a web-based platform for viewing and editing Office documents, this vulnerability could be leveraged by attackers who can trick users into opening crafted Excel files, potentially exposing sensitive data residing in memory buffers during file processing.

For European organizations, the impact of CVE-2025-48812 can be significant in environments where Microsoft Office Online Server is deployed to facilitate collaborative document editing and sharing. The vulnerability could lead to unauthorized disclosure of sensitive information stored in memory, such as fragments of documents, credentials, or other confidential data processed by the server. This risk is heightened in sectors handling sensitive or regulated data, including finance, healthcare, government, and critical infrastructure. Since the attack requires local access and user interaction, the threat vector is somewhat limited to insider threats or social engineering attacks that induce users to open malicious Excel files via the Office Online Server interface. However, given the widespread use of Microsoft Office products in Europe and the integration of Office Online Server in enterprise environments, exploitation could lead to data breaches, loss of confidentiality, and potential regulatory non-compliance under GDPR. The absence of known exploits currently reduces immediate risk, but organizations should act proactively to mitigate potential future exploitation.

To mitigate CVE-2025-48812 effectively, European organizations should: 1) Monitor Microsoft security advisories closely and apply patches or updates as soon as they become available, even though no patch is currently published. 2) Restrict local access to Office Online Server hosts to trusted administrators and users only, minimizing the risk of local exploitation. 3) Implement strict file upload and content filtering policies to detect and block potentially malicious Excel files before they reach the Office Online Server environment. 4) Educate users about the risks of opening untrusted or unexpected Excel documents via the Office Online Server interface to reduce the likelihood of user interaction-based exploitation. 5) Employ application-layer security controls such as sandboxing or containerization for Office Online Server to limit the impact of memory disclosure vulnerabilities. 6) Conduct regular security audits and memory analysis to detect anomalous information disclosure attempts. 7) Use network segmentation to isolate Office Online Server from sensitive backend systems to reduce lateral movement in case of exploitation.